Studies in this laboratory resulted in the development of an esophageal collection procedure in rats which permits the serial collection of all material (particles, phagocytes, mucous, etc.) removed from the lungs via the tracheal orifice and swallowed. Based on this procedure we have developed techniques for measuring: (1) the tracheobronchial clearance rates of particles from the lungs, (2) the velocity of the mucociliary escalator in the trachea, (3) the numbers of pulmonary macrophages leaving the lungs via the tracheal orifice, and (4) the functional role of pulmonary macrophages in transporting particles from the lungs to the oropharynx. These methods provide in vivo data in the rat without requiring surgery on any portion of the pulmonary system. Our research objectives are to characterize these parameters and their interrelationships under normal conditions and under various conditions of stress (dusts, noxious gases, bacteria and metabolic stimuli) to the pulmonary system. We hope to achieve an understanding of the basic physiological and homeostatic mechanisms which apply in mammals to the clearance of particulates from the lungs and to utilize this information in the realistic appraisal of the hazard associated with the inhalation of respirable dusts and air pollutants in man.